Lazy loading an array

[dswitzer]

I have a template in which I'd like to expose an ArrayList to the template, but I want to lazy load the array since it's not going to be commonly used and can be expensive to generate.

From the best that I can tell, lazy loading only works with objects that will create a Map so the only strategy for lazy loading an array would be to actually create a map that returns the array as a key. So my context would have to look something like:

Entity.History.Items

So I can have History value be a POJO or implementation of LiquidSupport, but I have to return a Map, so the actual array needs to be in another key (i.e. Items).

However, I'd really like to just use Entity.HistoryItems and have HistoryItems be a lazy loaded array.

Is there anything I'm missing? Is there a technique I'm missing which would allow any request to HistoryItems to lazy load and have it return any type of object?

For example, maybe the value of a specific key is a String/Long/etc that is just costly to calculate, so you only want to expose it if the user needs it. For example, we do some duration calculations that take working hours into account, which is extremely expensive to calculate. So ideally I'd only generate that information if it's actually needed.

The only other strategy I could think of was to parse the template first, find out which context keys are being requested and then only return the context needed. However, that's not a strategy I think will scale well and it's one I'd like to avoid.

[h0jeZvgoxFepBQ2C]

I'm also looking for a solution like this..

[dswitzer]

The solution we settled on was to create a "List" context for all array-like entities. This is an object that implements the LiquidSupport and represents an ArrayList, which when the toLiquid() method is called returns a HashMap with the following keys:

• Count - The size of the array.
• Items - The array.

Since we're returning an HashMap, it allows us to Lazy load the array and provides a convenience of exposing the array size.

[h0jeZvgoxFepBQ2C]

Hm I see, you wouldnt want to share this code or? :D

[dswitzer]

Nothing to share, but take a look at this in the docs:

https://github.com/bkiers/Liqp?tab=readme-ov-file#liquidsupport-example

You basically just need class that implements LiquidSupport with a toLiquid() method. Something like:

class LazyList implements LiquidSupport {
	private List<Object> list;

	public LazyList(List<Object> list) {
		this.list = list;
	}	

	@Override
	public Map<String, Object> toLiquid() {
		Map<String, Object> results = new HashMap<>();

		results.put("count", this.list.size());
		results.put("items", this.list);

		return results;
	}
};

Any time you want a lazy loaded list, you use the LazyList class as a wrapper for your ArrayList.